The present invention relates to a cooling structure of a multi-cylinder engine, which includes a cylinder block formed with a plurality of cylinders and a water jacket surrounding a cylinder bore wall of the cylinders.
Conventionally, as a cooling structure of an engine, a structure is known, in which a water jacket is formed in a cylinder block to surround a cylinder bore wall and a coolant fed from a water pump is introduced into the water jacket to cool the engine.
Moreover, to improve cooling performance and the like, providing a spacer member inside the water jacket to define an internal space of the water jacket has been discussed. JP4547017B discloses such a structure. Specifically, in the structure of JP4547017B, an introduction section for introducing a coolant fed from a water pump into a water jacket is provided in a cylinder block, and a spacer member provided with a plate-shaped restricting member opposing an opening of the introduction section and extending in up-and-down directions of the cylinder block is accommodated in the water jacket. In this structure, when the coolant flows into the water jacket from the introduction section, the coolant is suppressed from flowing to an intake-side part of the cylinder block and the cylinder head side without passing through an exhaust-side part of the cylinder block, and thus, a flow rate of the coolant flowing through the exhaust-side part of the cylinder block is secured, which leads to efficiently cooling the engine.
According to the structure of JP4547017B, it can be thought that the exhaust-side part of the cylinder block where the temperature easily becomes comparatively high can be efficiently cooled and a temperature difference between the exhaust-side and intake-side parts can be reduced. However, with this structure, a temperature difference between cylinders which occurs when the coolant flow inside the water jacket is stopped while the water pump is driven cannot be reduced, which causes a disadvantage of varying combustion states between the cylinders due to the temperature difference.
Specifically, in a case where a water pump which is forcibly driven by the engine is used as the water pump for feeding the coolant to the water jacket, even if the coolant flow inside the water jacket is stopped by, for example, closing an exit of the water jacket so as to increase the temperature of the cylinders and the like, the water pump is driven due to an operation of the engine, creating a state where the coolant is stirred near a part of the water jacket communicating with the water pump but is not stirred in other parts. Thus, the temperature difference occurs between a cylinder near a part communicating with the water pump and a different cylinder. In other words, near the part communicating with the water pump, due to the stirring, a high temperature coolant existing in a part of the cylinder block on the cylinder head side where the temperature is high in the cylinder block (i.e., the part close to a combustion chamber) causes a convective flow with a comparatively low temperature coolant existing in a part on an opposite side from the cylinder head (i.e., the part far from the combustion chamber). Therefore, the temperature of the part of the cylinder near the combustion chamber becomes lower than the other cylinders, and the temperature of the part of the cylinder far from the combustion chamber becomes higher than the other cylinders.